Single trench repair method with etched quartz for attenuated phase shifting mask

ABSTRACT

In accordance with the objectives of the invention a new method is provided for the repair of an attenuated phase shifting mask having a contact pattern. The invention etches a single trench in the quartz substrate of the phase shifter mask and removes the impact of a void in the phase shifter material. Alternatively, the invention provides for first conventionally restoring the original dimensions of a contact hole in which a pinhole is present and then etching a single or a double trench in the exposed substrate of the restored contact opening.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The invention relates to the fabrication of integrated circuit devices,and more particularly, to a method of creating an attenuated phaseshifting mask by methods of repair thereof, whereby effects of pinholesare removed.

(2) Description of the Prior Art

During and for the fabrication of semiconductor devices opticalprojection tools are an integral part of the optical lithographytechnology that is fundamental to the creation of semiconductor devicesand devices features. The optical projection tools conventionallycontain an electromagnetic light source, a configuration of lenses andan optical projection mask that contains a replica of the image that isto be created. The image of the mask is, with the interference and thehelp of the configuration of lenses, projected onto the surface overwhich the image contained in the mask is to be created.

Semiconductor device improvements are traditionally and consistentlyachieved by sharp reductions in device feature dimensions, resulting inincreasing device densities, which imposes on the supporting opticallithography technology the need for a continuing ability to provideimages of smaller dimensions while maintaining image resolution.

Conventional photolithography masks are limited in this respect due tothe increasingly smaller distance between adjacent light projections,which causes increased interference between closely spaced lightprojections. This has led to the development of phase-shifting masks,where effects of closeness of projecting light rays are cancelled bycontrolling the relative phase relationship between closely adjacentrays of light.

A phase shifting mask is provided with a layer of phase shifter materialthat is created in a pattern over the substrate of the mask. Thepatterned layer of phase shifter material causes the light that passesthrough the layer of phase shifter material to be out-of-phase by 180°with respect to the light that passes through the substrate over whichthe patterned layer of phase shifter material has been created. Thisresults in a corrective action between the light that passes through thetransparent substrate of the phase shifter mask and the light thatpasses through the layer of phase shifter material, this correctiveaction allowing further reductions in the images that are created usingthe phase shifter mask. Optionally, a phase shifter mask may also beprovided with a patterned layer of opaque material such as chrome tofurther enhance the mask application.

Phase shifting masks are generally created using methods ofphotolithography. These methods at times lead to the introduction offabrication defects in the surfaces of the created mask. For a phaseshifter mask to be operational, especially considering thedeep-submicron device features that must be created using the phaseshifter mask, surface irregularities, such as voids occurring in a layerof phase shifter material, must be prevented or corrected if present.Any surface irregularity that occurs in any of the layers of the phaseshifter mask, including the substrate of the phase shifter mask, resultsin a disruption of the there-through transmitted light and therefore inan interruption of a coherent interaction between the phase controlledlight that is transmitted through the phase shifter mask.

Cost considerations relating to the creation of phase shifter masks leadto the need for repairing phase shifter masks that show any defects thatmay negatively affect the desired performance characteristics of thephase shifter mask. The invention addresses this concern and provides amethod for the repair of attenuated phase shifter masks with a contactpattern.

U.S. Pat. No. 6,159,641 (Baume et al.) shows a method for repairingmasks.

U.S. Pat. No. 6,016,357 (Neary et al.) discloses a method to repairPSMS.

U.S. Pat. No. 6,114,073(Yang) shows a method to repair PSMS.

U.S. Pat. No. 5,272,024 (Lin) discloses a structure and method for PSMrepair.

U.S. Pat. No. 6,361,904 B1 (Chiu) shows a method for repairing theShifter Layer of an alternating phase shifter mask.

SUMMARY OF THE INVENTION

A principle objective of the invention is to repair an attenuated phaseshifting mask in a cost-effective manner.

Another objective of the invention is to repair an attenuated phaseshifting mask without impairing operational phase shifting requirementsof the mask.

Yet another objective of the invention is to repair an attenuated phaseshifting mask that is independent of the wavelength for which the maskis designed and used.

In accordance with the objectives of the invention a new method isprovided for the repair of an attenuated phase shifting mask having acontact pattern. The attenuated phase shifting mask is frequently usedfor the creation of contact holes or via openings and as such has asurface area of no phase shift and a surface area of 180° phase shift.Conventionally, when a surface defect such as a pinhole occurs in thelayer of phase shifter material of an attenuated phase shifter mask, anopaque material is deposited over the pinhole. This opaque materialhowever interrupts the desired and conventional operationalcharacteristics of light transmission of the attenuated phase shiftermask. To avoid such an interruption, the invention etches a singletrench in the surface of the quartz substrate of the phase shifter maskand removes the impact of a void in the phase shifter material.Alternatively, the invention provides for first conventionally restoringthe original dimensions of a contact hole in which a pinhole is presentand then etching a single or a double trench in the exposed substrate ofthe restored contact opening.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a through 1 c highlight conventional methods of repairing apinhole in a layer of phase shifter material.

FIGS. 2 through 5 highlight characteristics of phase shifting and lighttransmission for various combinations of deposition of opaque materialand the creation of single and double trenches etched in the surface ofthe quartz substrate of the attenuated phase shifter mask.

FIGS. 6 a and 6 b show a normal attenuated phase shifter mask in whichno pinhole is present.

FIGS. 7 a and 7 b show the occurrence of a pinhole in a contact opening.

FIGS. 8 a and 8 b show the conventional repair of a pinhole bydepositing a layer of material around the perimeter of a contact openingin which the pinhole is present.

FIGS. 9 a and 9 b show a first repair of the invention by providing asingle trench etch, in the exposed surface of the substrate (of theattenuated phase shifter mask) of the contact opening in which thepinhole is present.

FIGS. 10 a and 10 b show a second repair of the invention by providing adouble trench etch in the exposed surface of the substrate (of theattenuated phase shifter mask) of the contact opening in which thepinhole is present.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First are highlighted a number of statements of purpose that relate tothe invention:

-   1. attenuated phase shifter masks are used for the patterning of    layers of contact openings-   2. conventionally, a commercial repair apparatus is used to deposit    an opaque material over a pinhole defect in a layer of phase shifter    material; this layer of opaque material however is in the    application of a phase shifter mask equal to an opaque layer, such    as a layer of chrome, and does therefore not provide a phase shift    of 180 degrees to light passing through the attenuate phase shifter    mask-   3. if the surface of a quartz substrate is etched, the phase    shifting function of the attenuated phase shifter mask is maintained    around the perimeter of the contact openings, and-   4. it is the observed conclusion of the invention that, in order to    repair a pinhole defect in a contact area, a single trench etched in    the surface of the quartz substrate can be created such that a phase    shift of 180 degrees can be provided to light passing through the    attenuated phase shifter mask.

A conventional method of repairing a pinhole over the surface of aquartz substrate, which is used as the substrate for an attenuated phaseshifter mask, is first highlighted using FIGS. 1 a through 1 c for thispurpose.

The cross section that is shown in FIG. 1 a shows a substrate 10,conventionally comprising quartz, over the surface of which a layer 12of phase shifter material, such as MoSiON, has been deposited. The layer12 of MoSiON has been patterned and etched, creating an opening 11through the layer 12 of MoSiON, exposing the quartz substrate 10. Thephase shifting material 12 provides a 180° phase shift to the light thatpasses through this layer 12, the phase of the light that passes throughthe quartz substrate 10 without passing through the layer 12 of phaseshifter material is not affected and therefore has a 0° phase shift.

Pinhole 14 in the layer 12 of phase shifter material must be repaired, arepair that conventionally is performed by, as shown in the crosssection of FIG. 1 b, depositing a small amount 16 of opaque materialover the pinhole 14. This method has a number of disadvantages since theopaque material 16 acts as a deposition of chrome and therefore affectsthe light transmission characteristics of the layer 12 over which theopaque material 16 is deposited.

Some of the important parameters of light transmission and phaseshifting that are provided by an attenuated phase shifter mask are nowhighlighted, using parameters that have been highlighted in FIG. 1 a forthis purpose, as follows:

for regions 18, which are the regions of the attenuated phase shiftermask underlying the opening 11 created through the layer 12 of phaseshifter material, the light transmission of the light provided by lightsource 13 is about 100%, the phase shift that is introduced to thislight is about 0°, and

for regions 20 and 22, underlying the patterned and etched layer 12 ofphase shifter material, these parameters are: light transmission ofabout 6%, phase shifting of about 180°.

From the cross section that is shown in FIG. 1 b, it can be seen thatthese characteristics are disturbed for region 24, underlying thedeposited layer 16, where for region 24 the light transmission has beenreduced while the phase shift is difficult to predict.

As a further demonstration of the repair that is conventionallyperformed to repair a pinhole in the layer of phase shifter material,FIG. 1 c shows a cross section wherein the phase shifter material 12 hasbeen symmetrically removed around the perimeter of the contact opening11. The removed phase shifter material has been replaced with opaquematerial 16′. The replacement opaque material 16′ is known to peel fromthe surface of the substrate 10 over which it has been deposited.

To avoid the above indicated negative effects that are introduced byconventional methods of repairing a pinhole or any other opaquedeficiency over the substrate 10 of an attenuated phase shifter mask,the invention provides for etching a single trench into the substrate inareas surrounding the pinhole.

Comparisons of light transmission and phase shifting characteristics arefirst made for a number of configurations of quartz mask and thereoverdeposited layers of opaque material, using FIGS. 2 through 6 for thispurpose.

Referring first to the cross section shown in FIG. 2, this represents anormal attenuate phase shifter mask and is used to highlight therelation between phase shift and light transmission for the varioussurface regions of the conventional attenuated phase shifter mask.

Specifically highlighted in the cross section of FIG. 2 are:

10, the transparent substrate of the attenuated phase shifter mask,typically comprising quartz

12, the patterned and etched layer of phase shifter material, typicallycomprising MoSiON; other phase shifter materials that can be applied areCrO, ZrSiO₃ or SiON

11, the opening created through the layer 12 of phase shifter material,exposing substrate 10

18, the region of the substrate 10 that aligns with opening 11, ightpasses through the attenuated phase shifter mask confined by region 18,a 0° phase shift is experienced by the light that passes through theattenuated phase shifter mask that is bounded by opening 11

regions 20 and 22, phase shift about 180°, about 6% of the incidentlight that strikes the surface of layers 12 passes through these layers.

Referring now to the cross section that is shown in FIG. 3, there isshown:

10, the transparent substrate of the attenuated phase shifter mask,typically comprising quartz

20, the patterned and etched layer of opaque material

21, the opening created through the layer 20 of opaque material,exposing substrate 10

22, the region of the substrate 10 that aligns with opening 21, 100%light passes through the attenuated phase shifter mask confined byregion 22, a 0° phase shift is experienced by the light that passesthrough the attenuated phase shifter mask that is bounded by opening 21

regions 24 and 26, phase shift is difficult to control and predict, noincident light passes through the patterned layer 20.

Referring now to the cross section that is shown in FIG. 4 which shows asingle trench etched in the surface of the quartz substrate, there isshown:

10, the transparent substrate of the attenuated phase shifter mask,typically comprising quartz

20, the patterned and etched layer of opaque material

31, an opening created through the layer 20 of opaque material, exposingthe surface of substrate 10

33, a single trench etched in the surface of substrate 20

regions 34 and 36, phase shift is difficult to control and predict, noincident light passes through layers 20

regions 35 and 37, phase shift is zero, incident light passes 100%through the substrate 10

regions 32, phase shift 180 degrees, incident light passes 100% throughthe substrate 10.

Referring now to the cross section that is shown in FIG. 5, whichrepresents a double trench etched in the surface of the quartzsubstrate, there is shown:

10, the transparent substrate of the attenuated phase shifter mask,typically comprising quartz

20, the patterned and etched layer of opaque material

41, an opening created through the layer 20 of opaque material, exposingsubstrate 10

43, two trenches etched in the surface of substrate 20

regions 44 and 46, phase shift is difficult to control and predict, noincident light passes through the patterned layer 20

regions 45 and 47, phase shift is 180 degrees, incident light passes100% through the substrate 10

region 42, phase shift 180 degrees, incident light passes about 100%through the substrate 10.

From the above a number of relevant observations can be made.

Relating to the single trench etch as shown in the cross section of FIG.4, the following applies:

-   -   the etched area 33 is centered within the area of the contact        pattern, which is represented by opening 31 created through the        layer 20 of opaque material    -   the etched width of the etched single trench 33 approaches the        critical diameter of the contact area, exposed through the        opening 31    -   the etching of the quartz substrate is limited to a one-time        etch per contact area    -   the width of the etched trench exceeds the combined width of the        double trenches, which are shown in the cross section of FIG. 5    -   compared to the etching of the double trenches (43, shown in the        cross section of FIG. 5), the etching of the single trench (33,        shown in the cross section of FIG. 4) is easy to control in etch        width and etch location, and    -   relative to the deposited material 20 in combination with the        double trench etch, the single trench etch can be expected to        provided a larger repair window.

Relating to the double trench etch as shown in the cross section of FIG.5, the following applies:

-   -   the etched area 43 is at the edge of the contact pattern, which        is represented by opening 41 created through the layer 20 of        opaque material    -   the etched width 45/47 of the etched single trench 43 is smaller        than the critical diameter of the contact area, exposed through        the opening 41, a suitable combined etch width 45/47 must be        experimentally determined    -   the etch of the double trenches 43 must be located around the        perimeter of the contact pattern 41    -   the width (45+47, shown in the cross section of FIG. 5) of the        etched double trenches 43 is less than the width (32, shown in        the cross section of FIG. 4) of the single trench 33    -   compared to the etching of the single trench 33, the etching of        the double trenches 43 is difficult to control in etch width and        etch location, and    -   the etch of double trenches 43 requires four steps of etch from        which follows that the creation of the double trenches 43 is a        process that is more difficult to control.

The single trench etch is therefore the preferred method of repairing apinhole defect in the layer of phase shifter material as has beenhighlighted in the cross section of FIG. 4. That is the defect isassumed to be present in the region that is bounded by the opening 31over the surface of the quartz substrate, the etch therefore removes thephase shifter material from this surface region and further etches intothe surface of substrate 10, as has been highlighted in the crosssection of FIG. 4 with the trench 33 etched into the surface ofsubstrate 10. The phase relationships and light passing capabilitiesare, with the etch of trench 33, modified as follows:

The phase shift of 180° is achieved by selecting the depth of thecreated trench 33 such that, for a given incident light wavelength, anappropriate amount of quartz is removed. The light passing through theremaining layer of quartz underlying the created trenches can beprovided with a phase shift of 180° in this manner.

For instance, for an incident light wavelength of 248 nm, the thicknessof the quartz underlying the created trench must be about 238.5 nm. Foran incident light wavelength of 193 nm, the thickness of the quartzunderlying the created trench must be about 172.3 nm.

The following can be concluded:

for proper operation of a phase shifter mask, capabilities of lighttransmission and phase shifting must be controlled

in conventionally repairing a pinhole or a void in the phase shiftermaterial of a phase shifter mask, the pinhole is covered with an opaquematerial; where previously this region of the phase shifter material hasabout 6% light transmission and 180 degree phase shift, the repairedregion has 6% light transmission and unknown degree phase shift

by removing the phase shifter material that contains the pinhole or voidand by in addition etching into the surface of the quartz substrate, theeffectiveness of the phase shifter material is not altered since, seeFIG. 4 for the single trench etch, the required characteristics of 100%light transmission and 0 degrees phase shift are maintained for surfaceareas 35 and 37 while the etch for single trench 33, surface area 32,the light transmission characteristics through this surface are to still100% light transmission but now having, as determined by the depth ofthe trench 33, a 180 degree phase shift.

This latter alteration of the contact region, bounded by opening 31,does not detract from the functionality of the contact surface. Theexposure (of 100% light transmission) remains in effect over the entirecontact area while the light transmitted through region 32 of the quartzsubstrate has a not detrimental phase shift of 180 degrees.

The contact region will continue to be exposed (in light intensity) asdesired, the fact that the light within the area of exposure now has aphase shift of zero degrees and a phase shift of 180 degreesthere-within does not affect the exposure of the contact area. It would,if beneficially applied, further minimize negative effects of lightinterference within the exposed contact area.

For further clarification and extension of the invention, FIGS. 6 athrough 10 b are presented.

Shown in FIG. 6 a is a cross section of a substrate 10 of an attenuatedphase shifter mask over which a patterned layer 50 of shifter materialhas been created. Openings 51 created through the layer 50 of phaseshifter material are normal contact openings for pattern exposure byincident light 56. FIG. 6 b shows a top view corresponding to the crosssection of FIG. 6 a, the cross section shown in FIG. 6 a has been takenalong the line 6 a-6 a′ shown in FIG. 6 b. It is clear that the FIGS. 6a and 6 b relate to a normal pattern, that is a pattern in which nopinhole defect is present.

Shown in FIG. 7 a is a cross section of a substrate 10 of a attenuatedphase shifter mask over which a patterned layer 52 of shifter materialhas been created. Opening 51 created through the layer 52 of phaseshifter material is a normal contact opening for pattern exposure byincident light 56. Opening 53 created through the layer 52 of phaseshifter material is a contact opening in which a pinhole is present, asis obvious from the deformed and considerably larger diameter of opening53 when compared with the cross section of opening 51. FIG. 7 b shows atop view corresponding to the cross section of FIG. 7 a, the crosssection shown in FIG. 7 a has been taken along the line 7 a-7 a′ shownin FIG. 7 b.

Referring now to FIGS. 8 a and 8 b, therein is shown how a pinhole isconventionally repaired by deposition of an opaque material 54 aroundthe perimeter of opening 53, restoring the cross section of opening 53to a cross section 53′, which is equal to a cross section of the normalcontact opening 51.

As has previously been pointed out, the repaired contact opening 53′has, after the highlighted repair has been completed by the addition oflayer 54, lost the phase shifting function while at the same time thedepth of focus and the process window of the opening 53′ is smaller thanthe normal contact opening 51.

FIG. 8 b shows a top view corresponding to the cross section of FIG. 8a, the cross section shown in FIG. 8 a has been taken along the line 8a-8 a′ shown in FIG. 8 b.

Referring now to FIGS. 9 a and 9 b, there is shown how, in the structurethat has previously been discussed using FIGS. 8 a and 8 b, a singletrench 58 has been etched into the surface of substrate 10 where thesubstrate 10 is exposed in opening 53′, creating the opening 60 whichcomprises the single trench etch 58. For this method of repairing thepinhole 53, as shown in FIGS. 9 a and 9 b, the results are that thecontact created by the repaired opening 60 provides the required phaseshifting function while the depth of focus and the process window of theopening 60 are the same as the normal contact opening 51.

FIG. 9 b shows a top view corresponding to the cross section of FIG. 9a, the cross section shown in FIG. 9 a has been taken along the line 9a-9 a′ shown in FIG. 9 b.

The etch of double trenches is shown in FIGS. 10 a and 10 b, where inthe structure that has been discussed using FIGS. 8 a and 8 b, thedouble trenches 62 have been etched into substrate 10 where thissubstrate is exposed in opening 53′, creating the opening 60′, whichcomprises the double trench etch 62. The area highlighted as area 64 isthe area of the substrate 10 that is surrounded by the double trenches62.

For this method of repairing the pinhole 53, as shown in FIGS. 10 a and10 b, the results are that the contact created by the repaired opening60′ provides the required phase shifting function while the depth offocus and the process window of the opening 60′ is the same as thenormal contact opening 51.

FIG. 10 b shows a top view corresponding to the cross section of FIG. 10a, the cross section shown in FIG. 10 a has been taken along the line 10a-10 a′ shown in FIG. 10 b.

The cross sections and top views that are shown in FIGS. 6 a through 10b highlight:

a normal attenuated phase shifter mask in which no pinhole is present,FIGS. 6 a and 6 b

the occurrence of a pinhole in a contact opening, FIGS. 7 a and 7 b

the conventional repair of a pinhole, FIGS. 8 a and 8 b, by depositing alayer of material around the perimeter of a contact opening in which thepinhole is present

providing a single trench etch, FIGS. 9 a and 9 b, in the exposedsurface of the substrate (of the attenuated phase shifter mask) of thecontact opening in which the pinhole is present

providing a double trench etch, FIGS. 10 a and 10 b, in the exposedsurface of the substrate (of the attenuated phase shifter mask) of thecontact opening in which the pinhole is present.

Although the invention has been described and illustrated with referenceto specific illustrative embodiments thereof, it is not intended thatthe invention be limited to those illustrative embodiments. Thoseskilled in the art will recognize that variations and modifications canbe made without departing from the spirit of the invention. It istherefore intended to include within the invention all such variationsand modifications which fall within the scope of the appended claims andequivalents thereof.

1-30. (canceled)
 31. A repaired attenuated phase shifter mask,comprising: an attenuated phase shifter mask, the attenuated phaseshifter mask comprising a transparent substrate over which a patternedlayer of phase shifter material has been created; a defective area ofthe phase shifter material having been identified; the phase shiftermaterial having been removed from the defective area; opaque materialhaving been deposited on the defective area of the attenuated phaseshifter mask; and a single trench having been etched into thetransparent substrate aligned with the defective area to provide a phaseshift angle, the trench location and dimensions comprising an exposurepattern.
 32. The repaired attenuated phase shifter mask of claim 31, thetransparent substrate comprising quartz.
 33. The repaired attenuatedphase shifter mask of claim 31, a depth of the single trench being about238.5 nm for an exposure wavelength of 248 nm.
 34. The repairedattenuated phase shifter mask of claim 31, a depth of the single trenchbeing about 172.3 nm for an exposure wavelength of 193 nm.
 35. Therepaired attenuated phase shifter mask of claim 31, the phase shiftangle being about 180 degrees.
 36. The repaired attenuated phase shiftermask of claim 31, wherein said attenuated phase shifter mask is forcontact layer patterning.
 37. A repaired attenuated phase shifter mask,comprising: an attenuated phase shifter mask, the attenuated phaseshifter mask comprising a transparent substrate over which a patternedlayer of phase shifter material has been created; a defective area ofthe phase shifter material having been identified; the phase shiftermaterial having been removed from the defective area; and a doubletrench having been etched into the transparent substrate of theattenuated phase shifter mask aligned with the defective area to providea phase shift angle, wherein the double trench is located at an edge ofan exposure pattern, wherein the double trench further has dimensionsbeing smaller than dimensions of the exposure pattern.
 38. The repairedattenuated phase shifter mask of claim 37, the substrate comprisingquartz.
 39. The repaired attenuated phase shifter mask of claim 37, adepth of the double trench being about 238.5 nm for an exposurewavelength of 248 nm.
 40. The repaired attenuated phase shifter mask ofclaim 37, a depth of the double trench being about 172.3 nm for anexposure wavelength of 193 nm.
 41. The repaired attenuated phase shiftermask of claim 37, the phase shift angle being about 180 degrees.
 42. Therepaired attenuated phase shifter mask of claim 37, wherein saidattenuated phase shifter mask is for contact layer patterning.
 43. Arepaired attenuated phase shifter mask, comprising: an attenuated phaseshifter mask, the attenuated phase shifter mask comprising a transparentsubstrate over which a patterned layer of phase shifter material hasbeen created; a defective area of the phase shifter material having beenidentified; the phase shifter material having been removed from thedefective area; opaque material having been deposited on the defectivearea; and a double trench having been etched into the transparentsubstrate of the attenuated phase shifter mask aligned with thedefective area to provide a phase shift angle, wherein the double trenchis located at an edge of an exposure pattern, wherein the double trenchfurther has dimensions being smaller than dimensions of the exposurepattern.
 44. The repaired attenuated phase shifter mask of claim 43, thesubstrate comprising quartz.
 45. The repaired attenuated phase shiftermask of claim 43, a depth of the double trench being about 238.5 nm forexposure wavelength of 248 nm.
 46. The repaired attenuated phase shiftermask of claim 43, a depth of the double trench being about 172.3 nm forexposure wavelength of 193 nm.
 47. The repaired attenuated phase shiftermask of claim 43, the phase shift angle being about 180 degrees.
 48. Therepaired attenuated phase shifter mask of claim 43, wherein saidattenuated phase shifter mask is for contact layer patterning.